Physical Sciences Division Research Highlights

June 2006

Characterizing Nanoparticles Could Lead to More Efficient Carbon Tetrachloride Cleanup

Researchers at Pacific Northwest National Laboratory, the University of Minnesota, and Oregon Health and Science University discovered that smaller iron particles in permeable reactive barriers may better remediate groundwater contaminated with carbon tetrachloride.

Once common chemical now linked to health effects. In the past, carbon tetrachloride was a common component in refrigerants, industrial degreasers, and pesticides. From Air Force bases to dry cleaning solvent distribution facilities, sites across the United States are contaminated with this chemical, according to the Environmental Protection Agency. Exposure to high levels of carbon tetrachloride can damage the liver, kidney and nervous system.

In conventional remediation systems, micro-sized iron particles are pumped underground to create a barrier. The groundwater passes through the barrier, and the carbon tetrachloride is reduced to chloroform, which is toxic and environmentally undesirable.

Safer chemical byproducts, same speed. The team extensively characterized two iron nanoparticle preparations to determine if either offered significant advantages in remediation.

The first nanoparticles were synthesized by reduction of goethite with heat and hydrogen. The particles are called FeH2. With a diameter of 70 nanometers, the particles contained a mixture of α-iron particles coated with iron oxide and magnetite particles with some reduced sulfur.

The second nanoparticles were created by reductive precipitation with borohydride. The particles are called FeBH. The particles had a diameter of 10 to 100 nanometers.

The research team discovered that FeH2 broke carbon tetrachloride down more efficiently than FeBH. FeH2 produced more desirable cleanup by-products, while FeBH produced chloroform and behaved like the larger, micro-sized particles used in remediation today.

The research also showed that the smaller size of the particles did not increase the reaction rate. The overall rate of reaction with carbon tetrachloride did not change when the amount of iron was normalized to the external surface area of the particles.

Research to continue. Researchers continue to study why FeH2 was so effective in breaking down carbon tetrachloride. To date, the research is a focus of environmental scientists and others looking to develop more effective remediation techniques.

Nano particles created with borohydride, upper left, show similar chloroform yield during reduction of carbon tetrachloride as 150 micrometer particles, left and center of bottom graph. The nano particles created with hydrogen, upper right, generate about half the chloroform of the other two examples. The vertical range indicates results from a variety of test conditions.

The article on this research, entitled "Characterization and Properties of Metallic Iron Nanoparticles: Spectroscopy, Electrochemistry, and Kinetics" in Environmental Science & Technology in 2005, was the fourth most accessed article in the journal for the year. The article was written by Jim Amonette, John Linehan, and Klaus Pecher, from PNNL's Chemical & Materials Sciences Division along with PNNL's Don Baer, Chongmin Wang, and Dean Matson. The other authors were James Nurmi, Paul Tratnyek, and Vaishnavi Sarathy from Oregon Health and Science University and R. Lee Penn and Michelle Driessen from University of Minnesota.